Electrostatic coating apparatus



ELECTROSTATIC COATING APPARATUS Original Filed Sept. 29, 1945 INVENTOR. WILLIAM A. STARKEY BY ELECTROSTATIC COATING APPARATUS William A. Starkey, Columbus, Iud., .assiguor to Ransburg Eiectro-Coating Corp., Indianapolis, Ind., a corporafion of Indiana Original application September 29, 1945, Serial No. 619,371. Divided and this application October 8, 1951, Serial NO. 2505243 I 3 Claims. (Cl. 118 51) This invention relates to apparatus for the -electro-, static coating of articles and constitutesa division of my prior application Serial No. 619,371, filed September 29, 1945, now Patent No. 2, 632,716, issued March 24, 1953.

In coating articles electrostatically, it is common to move the articles successively past and in spaced relation to a discharge electrode while a spray of finely divided coating material is created in the space between the electrode and the articles moving past it. Through the aid of a suitable high voltage source, the articles and the electrodes are maintained at different potentials to create an electrostatic field between them. The potential difference maintained between the articles and the discharge electrode is sufiicient to cause the particles of coating materials to move under the influence of electric forces and become deposited on the articles.

In my prior application above referred to, I pointed out that in many instances the distribution of coating material over the surface of each article coated may depend upon the disposition of such articles with reference to other articles or to auxiliary electrodes of similar charge. I further disclosed that by suitably arranging the articles with reference to each other or with reference to auxiliary electrodes similarly charged it is possible to control the deposition of coating material over the surface of each article and either to reduce or increase, as desired, the relative quantity of coating material deposited on any portion of the articles surface. As further indicated in my prior application, the invention broadly disclosed therein may be employed to improve the uniformity of coating material distribution, when such uniformity is desired, or to effect a non-uniform distribution of coating material when such non-uniformity is desired.

The present invention is directed particularly to the control of the trajectory of the stream of coating material particles advancing toward a moving article to be coated, and even more particularly to an apparatus in which the auxiliary electrode is maintained in fixed position relative to the discharge electrode.

In carrying out the present-invention in a characteristic embodiment, there is provided means for moving a succession of articles over a predetermined path and means for creating a spray of finely divided electrically charged coating material particles and for directing the spray adjacent the path of article movement. The spray creating and directing means includes an ionizing electrode and a second electrode disposed at one side of the article path and in spaced relation to each other. A suitable source of high voltage maintains a substantial difierence of electrical potential between the second electrode and article on the one hand and the discharge electrode on the other hand. A spray gun, or its equivalent, emits a spray of finely divided coating material particles directed to pass through the resultant electrostatic field between the two electrodes and to intersect the article path. The two electrodes, and especially the ionizing electrode, are disposed td'be out of the stream of particled coating material ad- Y nited States Patent 0 Lil 2,711,155 Patented June 21, 1955 vancing toward intersection with the article trostatic deposition on the article.

"The invention will be described in greater detail in connection with the accompanying drawing in which is illustrated a preferred embodiment of the invention by-way of example, and wherein:

Figure 1 is a plan view of one embodiment ratus for carrying out the invention; and

Figure 2 is a side elevation view on line 22 of Figure 1.

Referring to Figures 1 and 2 of the drawing, there is path for elec of appa= shown a conveyor 10 for moving in the direction of are row 12 a plurality of articles 13, shown as flat metal sheets, over a predetermined path through a coating zone past and in spaced relation to oppositely disposed ionizing electrodes 14 and 15. Articles 13 are supported from the conveyor 10 by hangers 16 which, in accordance with the teaching of the parent application above referred to, also support strips 17 and 18 in spaced relation to the horizontal upper and lower edges respectively of the sheets 13. The strips 17 and 18 are of electrically conducting material.

Each of the ionizing electrodes 14 and-15 comprises an" from a supporting structure (not shown) by insulator rods 22 and 23 on opposite sides of and parallel to the path of article travel as shown in my U. S. Patent No. 2,425,652 issued August 12, 1947. I

The electrodes 14 and 15 may be connected in any suitable manner, as of'a suitable source of high voltage terminal of the voltage source conveyor 10. Thus through ground the articles 13 and 25. i The opposite the strips 17 and 18 are connected to such opposite'ter-.

minal of the high voltage source 25. In such an arrangement, the potential difference between the electrodes 14 and 15 on the one hand and the articles 13 and the strips 17 and 18 on the other establishes an electrostatic field between them.

'A plurality of spray guns 26, which preferably are of the air atomizing type, are suitably secured on a bracket (not shown) on one side of the conveyor 10 and are oriented so that the streams of coating material particles they discharge will intersect the article-path within the. In the particular apparatus" shown, which is designed to coat but one side of the sheets 13, both guns 26 are located on one side of the conveyor-e. g., the side occupied by the discharge el'ec-- trode 15.

in accordance with the present invention, the apparatus includes a fixed auxiliary electrode 28. Such electrode is maintained at a potential similar to that of the articles to be coated, and is spaced from the electrode 15 in such position that the stream of particled coating material advancing toward the article-path will pass through the electrostatic field existing between the discharge electrode 15 and the auxiliary electrode. As shown, the auxiliary electrode 2 8 is fixedly supported in position by, and.

grounded through, hanger 29 which in turn is afiixed a fixed portion of the conveyor lit).

In operation the sheets 13 on the conveyor 10 are moved successively over the predetermined path through the coating zone. Sprays of coating material particles from the spray guns 26 move through the field existing between the electrode 23 and the discharge electrode 15, acquire electrical charges of polarity similar to that of the discharge electrode, and are electrostatically deposited on the sheets 13. 7

by conductor 24, to one terminal 25 is grounded'as is the A distinguishing characteristic of the presentinvention is the fact that the initial effect of the electrostatic forces on the coating material particles is independent of the presence of articles 13in the coating zone. This is of advantage in that it promotes uniformity between the coating produced on the edges of the articles and the coating produced on surface portions more or less remote from edges. For example, in the arrangement illustrated, the particles of coating material, upon becoming charged, areattracted towardthe electrode 23, although carried past it by their momentum, and the particle-stream is thus electrostatically deflected toward the article path even when there are no articles in the coating zone. As a result, when the edge of an article enters the coating zone, the adjacent conditions in respect to the concentration of chargedparticles and to the movement of these-particles under the influence of electrostatic forces will not be greatly different from the conditions existing as other portions of the article pass through the coating zone.

The electrodes, and especially the discharge electrode,

are desirably located beyond the lateral limits of the stream of advancing coating material particles in order that they will receive none of the coating material, although deposition of some coating material on the aux iliary electrode will do no harm except for the consequent loss of coating material.

It is evident that to obtain a coating on both sides of the sheets 13 it would be necessary to dispose a set of spray guns on the opposite side of the conveyor 10 from the location of the guns 26. The use of such a second set of guns would not ordinarily necessitate the use of a second auxiliary electrode 28 on the other side of the article path.

The invention may be embodied in various other forms a coating zone and means for creating and controlling a spray of finely divided electrically charged coating material particles, said means comprising an ionizing electrode disposed at one side of the article-path, a spray gun for discharging a spray of finely divided liquid coating material past said ionizing electrode for interception by an article moving along such path, a second electrode positioned in fixed spaced relation to said ionizing electrode in the region of the spray as it advances toward the article and so disposed that such advancing spray will pass between the electrodes and generally ransverse to the lines of force of the field therebetween, said electrodes including portions lying on opposite sides of the advancing spray, and means including a high-voltage source electrically connected to said article and said electrodes for maintaining said electrodes and the article at such relative potentials that the coating material particles passing the ionizing electrode will become electrically charged and thereafter electrostatically deposited on the article.

.2. .Apparatnsior,electrostatically coating an electrically conducting article, said apparatus having a conveyor for conveying an article over a predetermined path through a coating zone and means for creating and controlling a spray of finely divided, electrically charged coating material particles, said means comprising an ionizing electrode disposed :at. one side of the article-path, a spray gun for discharging a spray of finely divided liquid coating material past said ionizing electrode for interception by an article moving along such path, means including a high voltage source electrically connected to said ionizing electrode and saidarticleformaintaining a difierence of elec trical potential-between said ionizing electrode and an 1 article in the coating zone whereby to create an electrostatic field between them, and a second electrode electrically connected to said high voltage source and positioned in fixed spaced relation to the ionizing electrode to reduce trodes and generally transversely to the lines of force of the field.

3. Apparatus for electrostatically coating'an electrically conducting article comprising means for moving the article over a predeterminedpath; means for creating a spray of finely divided electrically charged coating material particles and for directing the spray adjacent the path of article movement, said means including an ionizingj electrode disposed at one side of the article path and adjacent the spray anda second electrode positioned in fixed spaced relation to said ionizin'g'electrode and in the region of the spray, said second electrode being located 1 on the opposite side of the spray from said ionizing electrode so that'the spray will pass transversely through an electrostatic field maintained between said electrodes; and

means including a high voltage source electrically con:

nected to said articleand said electrodes for maintaining said electrodes and the article at relative potentials such that an electrostatic field will exist between said electrodes and such that the coating material particles passing through said field andthereby acquiring similar electric charges will be thereafter electrostatically attracted toward and deposited on the article.

References Cited in the file of this patent UNITED STATES PATENTS 2,270,341 Ransburg Jan. 20, 1942 2,421,787 Helrnuth June 10, 1947 2,427,652 Starkey Aug. 12, 1947 2,466,906 Miller Apr. 12, 1949v 2,486,877 Ransburg et a1 Nov. 1,1949 2,509,276 Ransburg May 30,1950 2,526,763 Miller Oct. 24,1950 2,551,035 Miller May 1, 1951' 7 2,632,716 Starkey Mar. 24, 1953 

1. APARATUS FOR ELECTROSTATICALLY COATING AN ELECTRICALLY CONDUCTING ARTICLE, SAID APPARATUS HAVING A CONVEYOR FOR CONVERYING AN ARTICLE OVER A PREDETERMINED PATH THROUGH A COATING ZONE AND MEANS FOR CREATING AND CONTROLLING A SPARY OF FINELY DIVIDED ELECTRICALLY CHANGED COATING MATERIAL PARTICLES, SAID MEANS COMPRISING AN IONIZING ELECTRODE DISPOSED AT ONE SIDE OF THE ARTICLE-PATH, A SPRAY GUN FOR DISCHARGING A SPRAY OF FINELY DIVIDED LIQUID COATING MATERIAL PAST SAID IONIZING ELECTRODE FOR INTERCEPTION BY AN ARTICLE MOVING ALONG SUCH PATH, A SECOND ELECTRODE IN TIONED IN FIXED SPACED RALATION TO SAID INOIZING ELECTROE IN THE REGION OF THE SPRAY AS IT ADVANCES TOWARD THE ARTICLE AND SO DISPOSED THAT SUCH ADVANCING SPRAY WILL PASS BETWEEN THE ELECTRODES AND GENERALLY TRANVERSE TO THE LINES OF FORCE OF THE FIELD THEREBETWEEN, SAID ELECTRODES INCLUDING PORTIONS LYING AN OPPOSITE SIDES OF THE ADVANCING SPRAY, AND MEANS INCLUDING A HIGH-VOLTAGE SOURCE ELECTRICALLY CONNECTED TO SAID ARTICLE AND SAID ELECTRODES FOR MAINTAINING SAID ELECTRODES AND THE ARTICLE AT SUCH RELATIVE POTENTIAL, THAT THE COATING MATERIAL PARTICLES PASSING THE IONIZING ELECTRODE WILL BECOME ELECTRICALLY CHARGED AND THEREAFTER ELECTROSTACTICALLY DEPOSITED ON THE ARTICLE. 